As there has been demand for increasing performance in semiconductor devices, there has also been a dramatic increase in the amount of heat generated by the semiconductor elements mounted on semiconductor devices. The same is true for semiconductor light emitting display devices such as semiconductor lasers, light emitting diodes, and the like. Therefore, the material onto which the semiconductor element is mounted preferably has the same coefficient of thermal expansion as the semiconductor element and has a high thermal conductivity. One example of a semiconductor device with an improved heat releasing construction is disclosed in Japanese Examined Patent Number 4-36473. This substrate is a composite material having main components of copper, tungsten, and molybdenum. Its coefficient of thermal expansion is close to that of the mounted semiconductor light emitting element at 5.0 to 8.5×10−6/K. In addition, its thermal conductivity is high at 200 W/m·K or greater. With the present invention, elements will be represented by their chemical symbols with copper as Cu, tungsten as W, and the like. In addition, with the invention disclosed in Japanese Laid-Open Patent Number 2002-232017, although the object of the invention is to improve the light emitting efficiency of the semiconductor device, the substrate, which is provided with a conductive part, is a flat board-shaped ceramic with a high thermal conductivity. However, depending on the field of application, with these semiconductor devices, including these types of light emitting devices, there is a demand for high output from the semiconductor element. As a result, there has been a trend toward increased size of the semiconductor element, and the amount of heat generation has also dramatically increased. Particularly with semiconductor devices with semiconductor light emitting elements, there has been a dramatic increase in the amount of light emission, and a concomitant increase in the size of the element and dramatic increase in the heat generation. As a result, there is a need for new means for improving the heat release efficiency around the heat generating area of the semiconductor device.